Demographic and lifestyle factors associated with body mass index among children and adolescents.

Cases of overweight and obesity among adults, adolescents, and children are escalating in the United States. Using data from the Continuing Survey of Food Intake for Individuals (CSFII) 1994-1996 and 1998, and the National Health and Nutrition Examination Survey III (NHANES), we developed multivariate regression models to examine the association between demographic and lifestyle variables (gender, race/ethnicity, age, family income, diet, and television viewing) and the body mass index (BMI) of children aged 6-11 years, and adolescents aged 12-19 years for CSFII and aged 12-16 years for NHANES. In the children's model, the statistically significant demographic predictors of BMI were age, race, gender, and family income. Among adolescents, the demographic predictors were age, race, and gender. Among the lifestyle variables, dietary factors were not associated with BMI in children. On the contrary, carbohydrates (less added sugars) had a statistically significant inverse relationship to BMI among adolescents. In both children and adolescents, television viewing was markedly associated with BMI, and participation in team sports was negatively associated with BMI. The overall process by which overweight develops is complex, and our four models explained only a small portion of total variance of BMI. The CSFII models explained 8.5% of the variance for children and 11.4% of the variance for adolescents. The NHANES models explained 8.8% of the variance for children and 12.5% of the variance for adolescents. Demographic variables accounted for roughly one-half of the explained variance for both children and adolescents. The rest of the explained variance was accounted for by television viewing, diet, and family income.